The present invention relates to a process for preparing a rubber containing polymer bound antidegradants. More specifically, the present invention relates to a process for forming a rubber comprising the aqueous emulsion polymerization of (a) at least one functionalized monomer that contains an antidegradant moiety and a polymerizable vinyl group with (b) at least one copolymerizable conjugated diene monomer, wherein the polymerization is conducted in the presence of an ester that functions as a synergist for the antidegradant, as a cosolvent/dispersing agent for the antidegradant during emulsion polymerization and as a plasticizer for the final polymer product.
Polymer bound antidegradants have been used in masterbatch rubber. The masterbatch rubber is blended down to the desired level with the rubber in which the antidegradant is intended to function. One route to prepare the masterbatch rubber involves the use of copolymerizable functionalized monomers. Many of these copolymerizable monomers are polar, high melting solids which are only slightly soluble in the copolymerizable diene monomers typically employed to prepare rubber. The solubility of these chemicals limits the level to which they can be polymerized and thus the extent to which they may be utilized in the masterbatch blending technique.
U.S. Pat. Nos. 3,658,769, 3,767,628 and 4,213,892 describe the preparation of compounds such as N-(4-anilinophenyl) methacrylamide and N-(4-anilinophenyl) acrylamide and the polymerization of such compounds with typical monomers. These references suggest that a solvent such as methylethyl ketone or isopropyl alcohol may be required to obtain adequate solubility of the monomers as well as to solubilize other ingredients. Unfortunately, the use of cosolvents like methylethyl-ketone (MEK) and isopropyl alcohol is limited in emulsion polymerization systems due to the tendency of these solvents to destabilize latex particles resulting in partial coagulation or the formation of multiple phases.
U.S. Pat. No. 4,521,574 discloses the use of dichloromethane (DCM) and/or tetrahydrofuran (THF) as cosolvents in an emulsion polymerization; however, DCM and THF have been determined to be a potential environmental and health concern.
U.S. Pat. No. 4,701,507 discloses the use of methyl isobutyl ketone (MIBK) as a cosolvent in an emulsion polymerization: however, MIBK is also unsuitable in many applications due to its odor and volatile nature. In addition, the use of a solubilizing cosolvent while necessary to dissolve polar, solid copolymerizable monomers in the emulsion polymerization recipe, most often will require its complete removal and economical recycle upon completion of the reaction. These steps of cosolvent addition, removal and recycle make their use inconvenient and costly.
U.S. Pat. Nos. 4,125,515, 4,241,217 and 4,301,296 disclose that esters such as 3,6,9-trioxyundecane-1,11-bis(3-n-dodecylthiopropionate) function as synergists when combined with polymer bound antioxidants. Examples of polymer bound antioxidants include N-(4-anilinophenyl) methacrylamide.
U.S. Pat. No. 4,216,116 discloses that esters such as 3,6,9-trixoyundecane-1,11-bis(3-n-dodecylthiopropionate) function as synergists with polymer bound phenolic antioxidants. Examples of phenolic antioxidants include the butylated reaction product of p-cresol and dicyclopentadiene.